Catheters for intraluminal treatment of a vessel section with ionizing radiation are used, for example, during or after percutaneous transluminal angioplasty, such as balloon dilatation or atherectomy of a stenosed blood vessel section, in order to prevent restenosis of this section. This is based on the theory that application of a defined dose of ionizing radiation can inhibit excessive cell proliferation triggered by the angioplasty and that by this means, restenosis of the treated vessel section can be avoided. A catheter of the generic type, however, can also be used for radiation treatment of other body cavities such as the esophagus or trachea or for treatment of the prostate.
A balloon catheter of the type mentioned in the introduction is known from EP 633,041 A1, in which a guide wire is arranged to be longitudinally displaceable in a central guide wire lumen of a two-lumen balloon catheter. An emitter of radioactive radiation in the form of a filament is incorporated into the tip of the guide wire. The second lumen serves as an inflation lumen for the balloon. Inflation of the balloon serves to radially center the radiation emitter positioned in the guide wire lumen in the vessel section that is to be treated. In this way, a radiation dose distribution is obtained uniformly about the circumference of the vessel wall. For applying the pressure to the balloon, a conventional liquid solution is used. The radiation source preferably used is yttrium-90, an easily screenable beta emitter with a half-life of 2.7 days, a mean electron energy of 0.942 MeV and a maximum electron energy of 2.28 MeV.
Over the greater part of its course from the emitter positioned in the balloon to the vessel wall to be treated, the radioactive radiation has to pass through inflation medium, in which process--as in any matter--radiation energy is absorbed. Thus, the energy dose available at the surface of the vessel wall, and the depth of penetration of the radiation into the vascular tissue at the wall, depend on the initial activity of the source, on the coefficient of absorption of the inflation medium, and on the length of travel of the radiation through the inflation medium.
The conventional liquid solution used to inflate the balloon includes saline and radiopaque contrast media which have a significant coefficient of absorption. Thus, known catheters of the type mentioned in the introduction suffer the drawback of long irradiation times, and consequently, long treatment times. Because of the necessary centering of the emitter in an inflated balloon, the flow of blood in the treated vessel has to be interrupted during this long treatment, which is undesirable.
The increasing importance of minimally invasive surgery and the treatment of ever narrower blood vessels demand guide catheters, and consequently balloon catheters, of ever smaller profile. Flexibility as well as longitudinal force and torsion transmission of the guide wire, balloon catheter and guide catheter must be guaranteed, as well as low friction between guide wire and balloon catheter. An adequately short deflation time for the balloon and a sufficiently large annular lumen for the flow of contrast medium are also necessary. If the inflation lumen is too narrow, the inflation medium can no longer flow quickly enough out of the balloon. A catheter with slow emptying of the balloon blocks the bloodstream for longer and thus, for example, also precludes the possibility of responding quickly to an ischemic reaction on the part of the patient during treatment.